A prior art method of forming a cord-reinforced tire structural member, such as a ply or a belt, disclosed in, for example, JP 2000-159399 A includes a coating process of coating cords with a rubber compound to form a cord-reinforced rubber belt, a cutting process of cutting the cord-reinforced rubber belt into strips of a length corresponding to the length of a section of a tire, and a tire structural member sheet forming process of successively arranging the strips such that the side edges of adjacent strips overlap each other to form a ply sheet or a belt sheet. The ply or belt sheet is wound in a large roll for storage. The large roll of the ply sheet or belt sheet is then sent to a ply or belt forming process. The ply or belt forming process cuts the ply sheet or belt sheet into plies or belts of a predetermined length conforming to the size of the tire.
The cords of the ply sheet wound in the large roll are arranged in the ply sheet so as to extend in a direction parallel to the axis of the tire. Since the cords are arranged at very small pitches slightly smaller than 1 mm, the pitches of the cords are liable to include errors. The ply sheet is cut into plies of a predetermined length corresponding to the circumference of the tire. Since errors in the pitches of the cords are accumulated in each of the plies, it is difficult to form the plies having the same number of the cords.
The pitches of the cords in the cord-reinforced rubber belt are determined by the coating step. There is a tendency that the cords are arranged in a higher density in edge parts of the cord-reinforced rubber belt. Consequently, the pitches of the cords are distributed irregularly in the plies.
The width of the cord-reinforced rubber belt is affected by variation of the line speed and rubber curing degree when operating conditions for the coating process are changed.
Thus, errors in the pitch of the cords of the ply sheet wound in the large roll tend to increase and hence it is very difficult to form the plies of the same length having the same number of cords.
The weight of the tire increases and material cost increases if the number of the cords in the plies is excessively large. The dynamic balance and the uniformity of the tire are deteriorated if the number of the cords deviates greatly from a predetermined number.
The present invention has been made in view of such problems and it is therefore an object of the present invention to provide a method of forming a cord-reinforced tire structural member, capable of easily forming a cord-reinforced tire structural member that is reinforced by a predetermined number of cords.